Serum and vascular endothelial growth factor (VEGF) deprivation has been shown to trigger apoptosis microvascular endothelial cells (MVEC). VEGF exerts its intracellular mitogenic and antiapoptotic effects after binding, activation and signaling through specific receptor (VEGFR) tyrosine kinase (RTK), including flt-1 (KDR) and flt-1. Several inhibitors of VEGF-RTK signaling have been recently developed and are undergoing clinical trials. Pre-clinical studies have demonstrated that these and other antiangiogenesis agents induce apoptosis of the MVEC in tumor xenografts which, in turn, results in apoptosis of tumor cells. Recent studies have also shown that exposure to the anticancer drug, paclitaxel, induces apoptosis of MVEC. In human MVEC, however, neither the molecular determinants nor the involvement of death receptor signaling has been carefully examined in the context of apoptosis induced by VEGF-RTK signaling inhibitors or paclitaxel. The overall objectives of this proposal are: 1) to investigate the effects of VEGF on molecular determinants of apoptosis of human dermal MVEC (HDMEC), including the mitochondrial permeability transition, cytosolic accumulation of cytochrome c, apoptosis activating factor (Apaf-1)-mediated caspase activity; as well as to determine the effect of these antiangiogenesis agents on the expression of the apoptotic regulators such as Bcl2, Al, BCl-XL, Bax, and Apaf-1; 2) to determine the effect of the enforced overexpression of Bax or Apaf-1, or conversely of Bcl-2, Bd-XL, Al and XIAP, on the molecular signaling and threshold for apoptosis in MVEC induced by the VEGF RTK inhibitors; additionally, the modulatory effect of the VEGF-RTK inhibitors versus VEGF on paclitaxel-induced anti-microtubule, cell-cycle and apoptotic effects would be determined in HDMEC; 3) to determine whether Fas death receptor and its apoptotic signaling alter the apoptotic threshold or are mechanistically involved in apoptosis of HDMEC due to VEGF-RTK inhibitors or paclitaxel. Collectively, these studies may help elucidate novel combinations of antiangiogenesis agents and the mechanisms of their apoptotic effect on MVEC, which results in tumor regression.